open函数用于文件处理
操作文件时，一般需要经历如下步骤：
- 打开文件
- 操作文件
一、打开文件
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文件句柄 = open('文件路径', '模式') |
打开文件时，需要指定文件路径和以何等方式打开文件，打开后，即可获取该文件句柄，日后通过此文件句柄对该文件操作。
打开文件的模式有：
- r ，只读模式【默认】
- w，只写模式【不可读；不存在则创建；存在则清空内容；】
- x， 只写模式【不可读；不存在则创建，存在则报错】
- a， 追加模式【不可读； 不存在则创建；存在则只追加内容；】
"+" 表示可以同时读写某个文件
- r+， 读写【可读，可写】
- w+，写读【可读，可写】
- x+ ，写读【可读，可写】
- a+， 写读【可读，可写】
"b"表示以字节的方式操作
- rb 或 r+b
- wb 或 w+b
- xb 或 w+b
- ab 或 a+b
注：以b方式打开时，读取到的内容是字节类型，写入时也需要提供字节类型
二、操作
1 class file(object)
2 def close(self): # real signature unknown; restored from __doc__
3 关闭文件
4 """
5 close() -> None or (perhaps) an integer. Close the file.
6
7 Sets data attribute .closed to True. A closed file cannot be used for
8 further I/O operations. close() may be called more than once without
9 error. Some kinds of file objects (for example, opened by popen())
10 may return an exit status upon closing.
11 """
12
13 def fileno(self): # real signature unknown; restored from __doc__
14 文件描述符
15 """
16 fileno() -> integer "file descriptor".
17
18 This is needed for lower-level file interfaces, such os.read().
19 """
20 return 0
21
22 def flush(self): # real signature unknown; restored from __doc__
23 刷新文件内部缓冲区
24 """ flush() -> None. Flush the internal I/O buffer. """
25 pass
26
27
28 def isatty(self): # real signature unknown; restored from __doc__
29 判断文件是否是同意tty设备
30 """ isatty() -> true or false. True if the file is connected to a tty device. """
31 return False
32
33
34 def next(self): # real signature unknown; restored from __doc__
35 获取下一行数据，不存在，则报错
36 """ x.next() -> the next value, or raise StopIteration """
37 pass
38
39 def read(self, size=None): # real signature unknown; restored from __doc__
40 读取指定字节数据
41 """
42 read([size]) -> read at most size bytes, returned as a string.
43
44 If the size argument is negative or omitted, read until EOF is reached.
45 Notice that when in non-blocking mode, less data than what was requested
46 may be returned, even if no size parameter was given.
47 """
48 pass
49
50 def readinto(self): # real signature unknown; restored from __doc__
51 读取到缓冲区，不要用，将被遗弃
52 """ readinto() -> Undocumented. Don't use this; it may go away. """
53 pass
54
55 def readline(self, size=None): # real signature unknown; restored from __doc__
56 仅读取一行数据
57 """
58 readline([size]) -> next line from the file, as a string.
59
60 Retain newline. A non-negative size argument limits the maximum
61 number of bytes to return (an incomplete line may be returned then).
62 Return an empty string at EOF.
63 """
64 pass
65
66 def readlines(self, size=None): # real signature unknown; restored from __doc__
67 读取所有数据，并根据换行保存值列表
68 """
69 readlines([size]) -> list of strings, each a line from the file.
70
71 Call readline() repeatedly and return a list of the lines so read.
72 The optional size argument, if given, is an approximate bound on the
73 total number of bytes in the lines returned.
74 """
75 return []
76
77 def seek(self, offset, whence=None): # real signature unknown; restored from __doc__
78 指定文件中指针位置
79 """
80 seek(offset[, whence]) -> None. Move to new file position.
81
82 Argument offset is a byte count. Optional argument whence defaults to
83 (offset from start of file, offset should be >= 0); other values are 1
84 (move relative to current position, positive or negative), and 2 (move
85 relative to end of file, usually negative, although many platforms allow
86 seeking beyond the end of a file). If the file is opened in text mode,
87 only offsets returned by tell() are legal. Use of other offsets causes
88 undefined behavior.
89 Note that not all file objects are seekable.
90 """
91 pass
92
93 def tell(self): # real signature unknown; restored from __doc__
94 获取当前指针位置
95 """ tell() -> current file position, an integer (may be a long integer). """
96 pass
97
98 def truncate(self, size=None): # real signature unknown; restored from __doc__
99 截断数据，仅保留指定之前数据
100 """
101 truncate([size]) -> None. Truncate the file to at most size bytes.
102
103 Size defaults to the current file position, as returned by tell().
104 """
105 pass
106
107 def write(self, p_str): # real signature unknown; restored from __doc__
108 写内容
109 """
110 write(str) -> None. Write string str to file.
111
112 Note that due to buffering, flush() or close() may be needed before
113 the file on disk reflects the data written.
114 """
115 pass
116
117 def writelines(self, sequence_of_strings): # real signature unknown; restored from __doc__
118 将一个字符串列表写入文件
119 """
120 writelines(sequence_of_strings) -> None. Write the strings to the file.
121
122 Note that newlines are not added. The sequence can be any iterable object
123 producing strings. This is equivalent to calling write() for each string.
124 """
125 pass
126
127 def xreadlines(self): # real signature unknown; restored from __doc__
128 可用于逐行读取文件，非全部
129 """
130 xreadlines() -> returns self.
131
132 For backward compatibility. File objects now include the performance
133 optimizations previously implemented in the xreadlines module.
134 """
135 pass
136
137 2.x
1 class TextIOWrapper(_TextIOBase):
2 """
3 Character and line based layer over a BufferedIOBase object, buffer.
4
5 encoding gives the name of the encoding that the stream will be
6 decoded or encoded with. It defaults to locale.getpreferredencoding(False).
7
8 errors determines the strictness of encoding and decoding (see
9 help(codecs.Codec) or the documentation for codecs.register) and
10 defaults to "strict".
11
12 newline controls how line endings are handled. It can be None, '',
13 '
', '
', and '
'. It works as follows:
14
15 * On input, if newline is None, universal newlines mode is
16 enabled. Lines in the input can end in '
', '
', or '
', and
17 these are translated into '
' before being returned to the
18 caller. If it is '', universal newline mode is enabled, but line
19 endings are returned to the caller untranslated. If it has any of
20 the other legal values, input lines are only terminated by the given
21 string, and the line ending is returned to the caller untranslated.
22
23 * On output, if newline is None, any '
' characters written are
24 translated to the system default line separator, os.linesep. If
25 newline is '' or '
', no translation takes place. If newline is any
26 of the other legal values, any '
' characters written are translated
27 to the given string.
28
29 If line_buffering is True, a call to flush is implied when a call to
30 write contains a newline character.
31 """
32 def close(self, *args, **kwargs): # real signature unknown
33 关闭文件
34 pass
35
36 def fileno(self, *args, **kwargs): # real signature unknown
37 文件描述符
38 pass
39
40 def flush(self, *args, **kwargs): # real signature unknown
41 刷新文件内部缓冲区
42 pass
43
44 def isatty(self, *args, **kwargs): # real signature unknown
45 判断文件是否是同意tty设备
46 pass
47
48 def read(self, *args, **kwargs): # real signature unknown
49 读取指定字节数据
50 pass
51
52 def readable(self, *args, **kwargs): # real signature unknown
53 是否可读
54 pass
55
56 def readline(self, *args, **kwargs): # real signature unknown
57 仅读取一行数据
58 pass
59
60 def seek(self, *args, **kwargs): # real signature unknown
61 指定文件中指针位置
62 pass
63
64 def seekable(self, *args, **kwargs): # real signature unknown
65 指针是否可操作
66 pass
67
68 def tell(self, *args, **kwargs): # real signature unknown
69 获取指针位置
70 pass
71
72 def truncate(self, *args, **kwargs): # real signature unknown
73 截断数据，仅保留指定之前数据
74 pass
75
76 def writable(self, *args, **kwargs): # real signature unknown
77 是否可写
78 pass
79
80 def write(self, *args, **kwargs): # real signature unknown
81 写内容
82 pass
83
84 def __getstate__(self, *args, **kwargs): # real signature unknown
85 pass
86
87 def __init__(self, *args, **kwargs): # real signature unknown
88 pass
89
90 @staticmethod # known case of __new__
91 def __new__(*args, **kwargs): # real signature unknown
92 """ Create and return a new object. See help(type) for accurate signature. """
93 pass
94
95 def __next__(self, *args, **kwargs): # real signature unknown
96 """ Implement next(self). """
97 pass
98
99 def __repr__(self, *args, **kwargs): # real signature unknown
100 """ Return repr(self). """
101 pass
102
103 buffer = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
104
105 closed = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
106
107 encoding = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
108
109 errors = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
110
111 line_buffering = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
112
113 name = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
114
115 newlines = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
116
117 _CHUNK_SIZE = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
118
119 _finalizing = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
120
121 3.x
三、管理上下文
为了避免打开文件后忘记关闭，可以通过管理上下文，即：
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with open('log','r') as f: ... |
如此方式，当with代码块执行完毕时，内部会自动关闭并释放文件资源。
在Python 2.7 及以后，with又支持同时对多个文件的上下文进行管理，即：
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with open('log1') as obj1, open('log2') as obj2: pass |